Hydraulic lift control system and valve therefor



R. D. CASSELL 3,072,107

HYDRAULIC LIFT CONTROL SYSTEM AND VALVE THEREFOR Jan. 8, 1963 6 3 3 2 55 V O 9 5 6 W 9 A V o 6 V 4 ix 4 m 4 M.-

u Q z m v Q INVENTOR.

ROBERT D. CASSELL QMIQW ATTORNEY Patented Jan. 8, 1963 3,072,107HYDRAULIC LEFT CUNTROL SYSTEM AND VALVE THEREFGR Robert D. Cassell,lnkster, Mich, assignor to Flowmatic Controls Incorporated, Birmingham,Mich, a corporation of Michigan Continuation of abandoned applicationSer. No. 839,202, Sept. 10, 1959. This application Mar. 16, 1961, Ser.No. 96,334

19 Claims. (Cl. 121-464) This application is a continuation ofpetitioners copending application Serial No. 839,202, filed September10, i959, and allowed September 20, 1960, now abandoned.

The present invention relates to an improved control system forhydraulic lifts and to an improved hydraulic pressure control valveadapted for use in such system.

An object of the invention is a system wherein the lift, when loweringby gravity, will have a maximum rate of descent which is low when thestatic load on the lift is great and is progressively higher as suchload is decreased. This is desired in order that the maximum rate ofdescent may be as high as possible without danger of damage when thelift is suddenly stopped. it is desired that the valve maintain thekinetic energy of the descending lift approximately constant,irrespective of the static load.

A further object of the invention is a hydraulic pres sure control valveof simple and inexpensive construction, capable of the above-statedcontrol function, and adapted for use in lift-control systems and alsoin other hydraulic systems wherein the control requirements are similar.

A problem in hydraulic control valves of the aforementioned type, andalso in others, is a damping means, capable of preventing surges in thecontrolled flow, which is non-clogging or self-cleaning, and is simpleand inexpensive in construction. An object of the invention is a valvehaving dash-pot damping means which will have these advantages and whichwill also compensate automatically for changes in pressure and inviscosity of the hydraulic fluid occasioned by temperature changes.

The foregoing and other objects and advantages wiil appear from thefollowing description of the preferred embodiments of the inventionshown in the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view of the lift control system, with thepressure control valve shown in detail in longitudinal section;

FlG. 2 is a fragmentary view of the valve with improved damper, the viewbeing partly in longitudinal section and partly in side elevation; and,

FIG. 3 is a fragmentary longitudinal section of a part of the valve ofFIG. 2, on an enlarged scale.

The lift comprises a cylinder it having slidable therein a piston 11connected to a platform 12 adapted to support a load L. The lift ismanually controlled by a valve 13 whose handle 14 is raised, to its fullline position, to raise the li t; is lowered to dotted line intermediateposition 14- to hold the lift elevated; and is lowered toward or to itsdash-dot line position 14;" to lower the lift at retarded or full speed.When the valve handle is raised, hydraulic fluid is drawn from sump 15by power-operated pump 16, and is directed by valve 13 through a conduit17, pressure control valve 18, and conduit 15 into the cylinder chamberbeneath the piston 11, to thereby raise the piston and platform 12 andthe load L thereon. The pressure in the system is limited by a reliefvalve 20. When the valve handle is in its intermediate position 14', thevalve 13 shuts off flow to and from conduit 17 and allows flow from thepump to discharge to the sump through conduit 21. Accordingly the liftis held against lowering. When the handle is lowered from position 14the valve 13 continues to allow fiow from the pump, but also aliows flowfrom conduit 17, through conduit 21 to the sump, the rate of flow fromconduit 17 depending upon how far the handle is moved from position 1toward position 14'. Accordingly the lift may lower by gravity at a ratedetermined by manual control of valve 13; or, if handle 14 is fullylowered so as to allow free discharge from conduit 17 into the sump,then at a rate that is determined by pressure control valve 18. Thisvalve has no control effect when the lift is being raised and isdesigned to impose little resistance to fluid flow under that condition.

Valve 18 comprises a sleeve or other housing 22 having a bore in which asubstantially cylindrical valve body 23 is disposed, being retained by asnap ring 24. The body has annular grooves 25 and 26 which, togetherwith the surrounding sleeve or housing, constitute annular fiuidpassages that are sealed by means of flexible O-rings 27. An axial bore28 in the left end of the body constitutes a cylinder in which a piston29 is slidable, the piston having a skirt 3%. The piston divides thecylinder 23 into a chamber 31, hereinafter called the inlet chamber(inasmuch as the entire purpose of the valve in. this system is thecontrol of exhaust flow from the lift cylinder iii), and a controlchamber 32 within the skirt 3t Conduit 19 communicates with chamber 31through an inlet opening 33 in the valve body. Conduit 1'7 communicates,through an outlet opening 34 in the opposite end of the body 23, with anaxial bore 35 in the body which constitutes the valves outlet chamber.

The piston 29 is urged to the left by a spring 36 toward the limitposition shown wherein it abuts a snap ring 37 which serves to hold thepiston and spring in assembly with the valve body. in the embodimentshown in FIG. 1 a disc 38 is interposed between the skirt of the pistonand the spring, to separate the control chamber 32 from the springchamber 39. The disc has an orifice it) therethrough, and, byrestricting fluid flow between the control chamber and the springchamber, serves to damp motion of the piston. In cases Where no suchdamping is needed the disc may be omitted entirely, in which event thespring 36 bears directly against the piston skirt 3t).

Fluid flow from inlet chamber '51 to the control chamber 32 is partiallythrough an orifice 41 in the head of piston 29, and also throughorifices 42 in the valve body into annular passage 25 and thence throughvalve ports 43 through the body and registering ports 5 i through thepiston skirt 30. Flow from the control chamber 3?. into outlet chamber35 is through registering valve ports 45 and 46, respectively throughthe piston skirt and the body, into the annular passage as, and thencethrough openings 47 through the body.

The openings 42 and 47 are large enough to impose no appreciablerestriction to iluid flow through the valve 18, while valve ports 43, 44and 45, 46 are designed to restrict fiow when the lift is descending bygravity with the manual control valve 13 open fully or nearly fully. Asthe lift descends, the restriction imposed by the variable-area orificecomprising ports 43, 44 and orifice 41 causes a pressure differential toexist between chambers 31 and 32 which tends to move the piston to theright against the resistance of spring 36, partially closing off theports 43 and 44. However, ports as are so proportioned and arranged asto present a smaller passage than orifice 4i and ports 43, so that uponan increase in the load L, and a consequent increase in the staticpressure in chamber 31 and in the compression of spring 36, the flowthrough the valve actually decreases.

Although the spring may of course be designed to provide whateversensitivity of control is needed for a particular application, thegeneral nature of the valves control action may be understood byassuming the spring to be so designed that it will exert a nearlyconstant load on the piston in all control positions of the piston.Since the spring load must always act to balance the pressuredifferential across the piston, it will be seen that under the assumedcondition the piston will so control the ports 46 as to maintain thisdifferential substantially constant, and, accordingly, that anyreduction in area of the fluid passages connecting the chambers onopposite sides of the piston wiil decrease the rate of flow through thevalve. Inasmuch as the fixed orifice 41 and the ports 43 controlled bythe piston together constitute a variable area orifice which decreasesas the piston moves to the right, it will be seen that the flow throughthe valve will decrease as the magnitude of load L is increased. If, asin practice, the spring load increases as the piston moves to the right,the pressure differential across the pistonwill increasecorrespondingly, but by suitable design of the orifice 41, 43,approximately the same control efiect described above may be obtained.

The valve ports 43, 46 and the orifice 41 are preferably so proportionedthat the velocity of the flow decreases in direct or nearly directproportion to increase in the square root of the static fluid pressurebeneath piston 11 and in inlet chamber 31. Thus irrespective of the loadL the valve 18 holds the kinetic energy at an approximately constantmagnitude, and when the lift bottoms or is stopped suddenly the maximumimpact is the same. This means that the lift can be lowered at themaximum speed consistent with safety under all loads.

The registering ports 43, 44 and the registering ports 4-5, 46 may beproportioned and arranged so that their respective effective areas areunchanged by rotation of the piston in the valve body. Otherwise,annular grooves as shown at 43 and 49 are provided around the pistonskirt lit to distribute fluid between ports 43 and 44 and between ports45 and 46.

As mentioned hereinbefore the disc 38 by having only restricted orifice4t} therethrough, and having a sliding fit with bore 28, restricts flowbetween chambers 32 and 3:9 and hence damps the action of the piston 2%,thus smoothing its pressure control effect.

A superior but also simple and inexpensive damper is shown in FIG. 2. Itcomprises a disc 5-1 of resilient material, preferably having asubstantially greater coefiicient of thermal expansion than the materialof which the valve body 23 is made. A clearance space 51 between theperiphery of the disc and the bore 28 constitutes a flowcontrol orificesimilar in function to orifice 4t). A crowned plate 52 interposedbetween the disc and spring 36 causes the spring pressure to be appliedto the center of the disc. Because of this, the disc is bowed more orless depending on the magnitude of the spring load and the pressuredifferential between chambers 32 and 39. Due to the edge thickness ofthe disc, such bowing has the effect of decreasing the clearance space51, thereby increasing the damping effect upon increase of both the loadL and dynamic loads (since these affect the pressure differentialbetween chambers 32 and 39). The effect of the bowing is shown, greatlyexaggerated, in FIG. 3, Where the disc appears in broken lines in itsbowed position wherein it decreases the clearance space 51. The edgethickness of the disc can of course be increased or decreased to varythe magnitude of such increase. Due to the greater thermal expansion ofthe disc, the clearance space 51 is decreased with rise in temperatureof the hydraulic fluid in the system, thereby compensating for thereduction in viscosity of the fluid which accompanies temperatureincrease. The relatively great circumferential dimension of the disc Stlreduces to a minimum the possibility of clogging of the clearance spaceor damper flow-control orifice 51, and the flexing of the disc duringoperation of the system constitutes a selfcleaning action tending todislodge foreign matter which might otherwise eventually clog thisorifice. In order that the plate 52 will not itself have a dampingeffect, a clearance space 53 substantially greater than clearance 51 isprovided between its periphery and the bore 28.

Having now described the preferred embodiments of my invention and theiroperation, what I claim is:

l. A hydraulic lift control system comprising a valve through whichfluid may flow to and from the lift cylinder when the lift is beingraised and lowered, the valve allowing free flow to the cylinder andlimiting the maximum rate of exhaust flow from the cylinder, said valvehaving a spring-backed piston movable in response to changes in exhaustfluid pressure upstream therefrom, said valve having variable-areaorifices so controlled by the piston as to decrease and increase in arearespectively upon increase and decrease in such pressure, whereby themaxirate of descent of the lift cylinder decreases as the static load onthe lift increases, said valve comprising a body having a cylinderdivided by said piston into an inlet chamber and a control chamber, withsaid inlet chamber arranged to receive exhaust fluid from the liftcylinder when the lift is lowering, and said valve body also having anoutlet opening for such exhaust fluid, the piston-backing spring beingarranged to resist motion of the piston in a direction to expand saidinlet chamber, a first variable-area orifice connecting the inletchamber with the control chamber, and a second variable-area orificeconnecting the control chamber with said outlet opening, the areas ofboth of said orifices being controlled by the piston and being decreasedby motion of the piston in said direction.

2. A control system according to claim 1 in which the area of the secondvariable-area orifice is decreased more rapidly than the firstvariable-area orifice upon motion of the piston in said direction.

3. A hydraulic valve comprising a body having inlet and outlet openingsand a cylinder, a piston dividing the cylinder into an inlet chambercommunicating with said inlet opening and a control chamber, a springarranged to resist motion of the piston in a direction to expand theinlet chamber, registering valve ports in the walls of the cylinder andpiston constituting a first variable-area orifice to control the fluidflow from the inlet chamber to the control chamber, and otherregistering valve ports in the walls of the cylinder and pistonconstituting a second variable-area orifice to control fluid flow fromthe control chamber to the outlet opening, both of said orificesdecreasing in area upon motion of the piston in said direction.

4. A valve according to claim 3 in which said valve ports are soarranged that said second variable-area orifice is constricted morerapidly than the first variable-area orifice upon motion of the pistonin said direction.

5. A valve according to claim 3 in which there are dash-pot means toimpede motion of the piston.

6. A valve according to claim 5 in which the dash-pot means comprises adisc interposed between the piston and the spring, said disc being ofsmaller diameter than the cylinder to provide an annular flow-controlorifice between the control chamber and the chamber containing saidspring, the peripheral portion of the disc bearing against the pistonand the spring being arranged to bear on the central portion of thedisc, whereby the disc is flexed to decrease the area of saidflow-control orifice as the spring load and pressure differential acrossthe disc increase.

7. A valve according to claim 6 in which the disc has a greatercoefficient of thermal expansion than the valve body, whereby the areaof said flow-control orifice is reduced upon temperature increase.

8. A hydraulic valve comprising a housing having a bore, a bodytelescoped in the bore having spaced annular grooves closed by the wallof the bore to define first and second fluid passages, said body havinginlet and outlet openings respectively in its opposite ends and alsohaving a cylinder which opens into said inlet opening, a

piston in said cylinder and means for limiting motion of the pistontoward said inlet opening, a spring in the cylinder for resisting motionof the piston in the opposite direction, said piston having a skirtextending from the head thereof away from said inlet opening anddefining a con trol chamber, registering valve ports in said body andskirt constituting a first variable-area orifice between said firstpassage and the control chamber, registering valve ports in said memberand skirt constituting a second variablerea orifice between the controlchamber and said second passage, both of said orifices decreasing inarea upon motion of the piston in said opposite direction, with the areaof the second orifice decreasing more rapidly than that of the firstorifice, and ports in said member connecting said second passage andsaid outlet opening.

9. A hydraulic valve comprising a body having a cylinder, a pistonslidable in the cylinder, a compression spring in the cylinder acting onthe piston, a disc interposed between the piston and the valve, saiddisc being of smaller diameter than the cylinder to allow restrictedfluid How to and from the spring chamber, the peripheral portion of thedisc bearing against the piston and the spring being arranged to bear onthe central portion of the disc, whereby the disc is fiexed to increasethe diameter thereof as the spring is compressed and the pressuredilferential across the disc is increased.

10. A valve according to claim 9 in which the disc has a greatercoefficient of thermal expansion than the valve body, whereby theeliective area between the disc and the cylinder wall is reduced upontemperature increase.

11. A valve according to claim 9 in which there is a plate interposedbetween the disc and the spring, said plate being of smaller diameterthan the disc and having a convex face contacting the central portion ofthe disc.

12. A valve according to claim 9 in which the piston has a skirt whoseedge engages the disc, the portion of the skirt adjacent the disc beingof smaller external diameter than the disc to provide an annular chamberbetween the skirt and the cylinder wall, and a fluid passage through thepiston into said annular chamber.

13. A hydraulic device comprising a body having a cylindrical chamber, aresilient circular disc disposed transversely of the chamber, the discbeing of slightly smaller diameter than the chamber and of finite edgethickness to provide an orifice around the periphery of the disc throughwhich fluid may pass from one side of the disc to the other and which isreduced in area upon flexure of the disc, and a support engageable withone face of the disc adjacent the periphery thereof whereby such fiexuremay occur upon application of pressure against the opposite face of thedisc.

14. A device according to claim 13 in which there is a transverselycrowned member movable relative to said support in a direction axial ofthe chamber for abutting and thereby applying said pressure to thecentral portion of said opposite face of the disc.

15. A hydraulic device comprising a body having a cylindrical chamber, aresilient disc disposed transversely of the chamber, the disc being ofslightly smaller diameter than the chamber and of finite edge thicknessto provide an orifice around the periphery of the disc through whichfluid may pass from one side of the disc to the other and which isreduced in area upon flexure of the disc, and a member supporting thedisc adjacent the center thereof for such flexure in response topressure applied against the area of the disc outwards of the supportedcenter thereof.

16. A device according to claim 15 in which said member is atransversely crowned plate engaging one face of the disc at the centralportion thereof, for supporting the disc for such flexure by pressureapplied against the opposite face thereof.

17. A device according to claim 16 in which there is a member having acircle of contact with said opposite face of the disc adjacent theperiphery thereof, for applying said pressure thereto.

18. A hydraulic lift system comprising a cylinder, a piston in saidcylinder, a load-bearing member supported by the piston and adapted tolower with the piston by gravity and to be raised by fluid pressure inthe cylinder beneath the piston, a valve through which fluid may flow toand from the cylinder, respectively to effect raising and to allowlowering of said member and piston, said valve aliowing free how to thecylinder from a source of hydraulic pressure but limiting the maximumrate of exhaust fiow from the cylinder to a sump associated with saidsource, said valve having a springbacked piston movable in response tochanges in exhaust fluid pressure upstream therefrom, said valve havingvariable area orifices so controlled by the spring-backed piston as todecrease and increase in area respectively upon increase and decrease insuch pressure, whereby the maximum rate of descent of thefirst-mentioned piston and said load-bearing member decreases as thestatic load thereon increases.

19. A hydraulic rift system comprising a cylinder, a piston in saidcylinder, at loadbearing member supported by the piston and adapted tolower with the piston by gravity and to be raised by fluid pressure inthe cylinder beneath the piston, a valve through which fluid may how toand from the cylinder, respectively to effect raising and to allowlowering of said member and piston, said valve allowing free fiow to thecylinder from a source of hydraulic pressure but limiting the maximumrate of exhaust flow from the cylinder to a sump associated with saidsource, said valve comprising a body having a cylinder and aspring-backed piston slidable therein, said valve cylinder being dividedby said valve piston into an inlet chamber and a control chamber, withsaid inlet chamber arranged to receive exhaust fluid from the liftcylinder when said load-bearing member is lowering, and said valve bodyalso having an outlet opening for such exhaust fluid, the piston-backingspring being arranged to resist motion of the valve piston in adirection to expand said inlet chamber, a first variable-area orificeconnecting the inlet chamber with the control chamber, and a secondvariable-area orifice connecting the control chamber with said outletopening, the areas of both of said orifices being controlled by thevalve piston and being decreased by motion of the valve piston in saiddirection.

References Cited in the file of this patent UNITED STATES PATENTS2,495,785 Stephens Jan. 31, 1950 2,676,573 Abbe Apr. 27, 1954 2,785,660Jaseph Mar. 19, 1957

1. A HYDRAULIC LIFT CONTROL SYSTEM COMPRISING A VALVE THROUGH WHICHFLUID MAY FLOW TO AND FROM THE LIFT CYLINDER WHEN THE LIFT IS BEINGRAISED AND LOWERED, THE VALVE ALLOWING FREE FLOW TO THE CYLINDER ANDLIMITING THE MAXIMUMU RATE OF EXHAUST FLOW FROM THE CYLINDER, SAID VALVEHAVING A SPRING-BACKED PISTON MOVABLE IN RESPONSE TO CHANGES IN EXHAUSTFLUID PRESSURE UPSTREAM THEREFROM, SAID VALVE HAVING VARIABLE-AREAORIFICES SO CONTROLLED BY THE PISTON AS TO DECREASE AND INCREASE IN AREARESPECTIVELY UPON INCREASE AND DECREASE IN SUCH PRESSURE, WHEREBY THEMAXIMUM RATE OF DESCENT OF THE LIFT CYLINDER DECREASES AS THE STATICLOAD ON THE LIFT INCREASES, SAID VALVE COMPRISING A BODY HAVING ACYLINDER DIVIDED BY SAID PISTON INTO AN INLET CHAMBER AND A CONTROLCHAMBER, WITH SAID INLET CHAMBER ARRANGED TO RECEIVE EXHAUST FLUID FROMTHE LIFT CYLINDER WHEN THE LIFT IS LOWERING, AND SAID VALVE BODY ALSOHAVING AN OUTLET OPENING FOR SUCH EXHAUST FLUID, THE PISTON-BACKINGSPRING BEING ARRANGED TO RESIST MOTION OF THE PISTON IN A DIRECTION TOEXPAND SAID INLET CHAMBER, A FIRST VARIABLE-AREA ORIFICE CONNECTING THEINLET CHAMBER WITH THE CONTROL CHAMBER, AND A SECOND VARIABLE-AREAOPENING, THE AREAS OF BOTH OF SAID ORIFICES BEING CONTROLLED BY THEPISTON AND BEING DECREASED BY MOTION OF THE PISTON IN SAID DIRECTION.